Examples: Added README into the Visual Studio solution to people are less likely to miss it.

examples/opengl3_example/opengl3_example.vcxproj

@@ -163,6 +163,9 @@
     <ClInclude Include="..\libs\gl3w\GL\glcorearb.h" />
     <ClInclude Include="imgui_impl_glfw_gl3.h" />
   </ItemGroup>
+  <ItemGroup>
+    <None Include="..\README.txt" />
+  </ItemGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
   <ImportGroup Label="ExtensionTargets">
   </ImportGroup>